Compass, particularly for orientation purposes



Dec. 14, 1943. M A JoNssoN 2,336,789

, COMPASS., PARTICULARLY FOR ORIENTATION PURPOSES A v Filed nay 7, 1942 Snow,

Patented Dec. ld, 1943 CQMPASS, PARTICULARLY FOR OREEN'IATION PURPOSES Arvid Jonsson, Mailing, Sweden Application Ivay 7, 1942, Serial No. 442,109 En `Sweden November 21, 194) Claims.

The present invention refers toimproved compasses of the type having their compass-boxes lled with a liquid, particularly so called orientation Compasses.

The principal object of the invention is to prevent the formation of air bubbles which are formed due to variations in temperature and pressure within the compass-box and which disturb the movements of the compass-needle and the reading of the compass. It has already been suggested to provide for an equalization of the pressure by using thin Celluloid in the Walls of the compass-box which have to be surrounded by a protective cover of metal to get suicient strength. In the rst place, this protective cover increases the production costs of the compass, and in the second place it conceals a part of the map on which the course is to be made out, so that making out the course becomes more dimcult. It has been found, however, that irrespective ci the provisions made air bubbles are yet sometimes formed in the compass-boxes.

Through the present invention the above disadvantages are wholly eliminated and the advantage achieved that no special bearing lines for the setting of the compass-box are needed on the latter. A protective cover is not required, because the walls cf the box can be made suiciently strong. The substantial characteristic of he invention is that the compass-box is provided with inwardly projecting thin-walled embossments or with tubes of Celluloid or other suitable material which are filled with air or other gaseous medium to provide for a pressure equalization in the liquid. The longitudinal edges of the embossments or tubes which, when arranged parallel to the north-south line of the compass-box, may serve as bearing lines in making out the course by turning the compass-box in the well-known manner so that said edges run parallel to a meridian on the map.

The invention will be more particularly described with reference to the accompanying drawing which illustrates two forms thereof,

Figure l being a horizontal view of a compass and Figure 2 a section along the line II-II in Figure l, while Figure 3 is a section similar to Figure 2 of a compass-box of a somewhat altered construction.

In the drawing, i designates a compass base which is formed as a rule and is preferably made of transparent material, e. g. Celluloid. At one end this base or rule has a circular opening 3 provided with a ledge 2. If the compass base is made of opaque material, e. g. Bakelite, there should be provided largerV rectangular or otherwise shaped openings d so as to expose as great parts as possible of the map. On the top side of the compass base i there is provided an annular disc il which surrounds the circular opening 3 and is provided with a graduation, the inner edge ii ci this disc projecting slightly beyond the side wall of the opening 3. In the opening i a compass-box 'l is rotatably mounted, and the edge ii of the disc 5 and the ledge 2 form a guide for a guiding flange d provided on the compass-box. For facilitating the rota-y tion of the compass-box I the top edge 9 thereof should be knurled in a Weil-known manner. For damping the oscillations of the compass needle l the compass-box l, whichv should preferably be of some transparent material, isl lled with oil or other suitable liquid. On the top side of the compass-box there is besides an index mark l2 (nortlvscuth mark).

The above described arrangements are wellknown, and the improvement of the present invention consists in the particular construction of certain means in the compass-box by which pressure equalization in the latter is made possible, as will be described in the following. In the form shown in Figures 1 and 2 this is achieved by the provision of parallel tubes Il which are closed at their ends, on either side of the pivot l@ within the compass-box. The tubes consist of Celluloid or other suitable yielding material and are hermetically closed and lled with air or other gaseous medium. rIhe liquid contained in the compass-box is thereby allowed to expand in the case of temperature differences, as the walls of the tubes Il are pressed in slightly by the liquid while compressing the enclosed gaseous medium. There is no longer any risk of the box l breaking due to pressure variations or of disturbing air bubbles being formed in the liquid.

In the bottom l5 of the compass-box in the modification of Figure 3 there are, on either-side of the pivot it, pressed up parallel embossments I8 which, if they are given suiiicient height, may serve as stops for limiting the oscillations of the compass-needle. Where the compass-box consists of Celluloid, Cellophane or other suitable yielding material the embossments I8 similarly as the tubes Il in Figures 1 and 2 besides serve the purpose of making unobstructed eX- pansion of the liquid within the compass-box possible. At the expansion of the liquid a compression or indentation of the parallel longitudinal walls i9 of each embossment I3 takes place, and at the equalization of the pressure they return to their original position. The longitudinal edges or Walls I9 which, as mentioned,

may be parallel with each other and with the north-south line of the compass-box may advantageously serve as bearing lines in making out the course.

Also the tubes l1 may be given such dimensions and be arranged in such a manner that they serve as stops of the compass-needle and as bearing lines in making out the course. If they should be liable to undergoing such a great deformation under the influence of a heavy compression that they would become inefdcienj; as bearing indicating means, they may be slightly countersunk in the bottom of the compass-box.

The forms of construction described above and ShOWn in the drawing are to be considered only as examples, as the invention is capable of being carried into effect also in other forms.

What I wish to secure by Letters Patent is:

1. In Compasses of the character described having their compass-box of transparent material so that a chart or the like is viewable therethrough, said compass-box being iilled with a liquid, the combination therewith of yielding means in direct Contact with the liquid in said compass-box, said yielding means comprising an elongated tubular element filled with a gaseous medium and secured to the compass-box so as to have its longitudinal edges parallel with the north-south line of the compass, thereby providing a bearing line as well as an expansion member for the purpose of equalizing the pressure of the liquid.

2. In Compasses of the character described having their compass-box of transparent material so that a chart or the like is viewable therethrough, said compass-box being lled with a liquid and having a needle mounted on a pivot therein, the combination therewith of hermetically closed tubes of yielding material mounted within the compass-box and lled with a gaseous medium, said tubes being arranged on each side of said pivot and in direct contact with the liquid in the compass-box, thereby providing expansion means for the purpose of equalizing the pressure of the liquid.

3. In Compasses of the character described having their compass-box of transparent material so that a chart or the like is viewable therethrough, said compass-box being lled with a liquid, the combination therewith of inwardly projecting yielding tubular embossments on the bottom wall of said compass-box, said embossments being in direct contact with the liquid in the compass-box and constituting bearing lines as Well as expansion means for the purpose of equalizing the pressure of the liquid, the interior of said embossments being in communication With the atmospheric air.

4. In Compasses of the character described having their compass-box of transparent material so that a chart or the like is viewable therethrough, said compass-box being lled with a liquid, the combination therewith of hermetically closed yielding tubes provided within the compass-box on either side of the compass-needle to serve as stops for the latter, said tubes being filled with a gaseous medium and being in direct contact with the liquid in the compassbox and constituting expansion means for the purpose of equalizing the pressure of the liquid.

5. In compasses of the character described having their compass-box of transparent material so that a chart or the like is viewable therethrough, said compass-box being lled with a liquid, the combination therewith of yielding means having longitudinal edges parallel with each other and with the north-south line of the compass, said yielding means being in direct Contact with the liquid in said compass-box and constituting bearing lines as well as expansion chambers for the purpose of equalizing the pressure of the liquid, the interior of said yielding means being in communication with the atmospheric air.

ARVID JONSSON. 

